Loans - Presentation of Loans Individually Evaluated for Impairment by Class (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	$ 13,645	$ 14,637	$ 13,645	$ 14,637	$ 12,801
With no specific allowance recorded, Recorded Investment	8,698	8,565	8,698	8,565	6,499
With no specific allowance recorded, Average Recorded Investment	7,088	8,111	6,892	8,038
With no specific allowance recorded, Interest Income Recognized	59	39	93	93
With no specific allowance recorded, Cash Basis Income Recognized	59	39	83	76
With a specific allowance recorded, Unpaid Principal Balance	17,444	15,820	17,444	15,820	14,768
With a specific allowance recorded, Recorded Investment	16,441	15,213	16,441	15,213	14,095
With a specific allowance recorded, Allowance for Loan Losses Allocated	1,816	1,661	1,816	1,661	1,201
With a specific allowance recorded, Average Recorded Investment	16,068	16,322	15,408	16,998
With a specific allowance recorded, Interest Income Recognized	281	183	544	421
With a specific allowance recorded, Cash Basis Income Recognized	279	180	485	361
Total Unpaid Principal Balance	31,089	30,457	31,089	30,457	27,569
Total Recorded Investment	25,139	23,778	25,139	23,778	20,594
Total Average Recorded Investment	23,156	24,433	22,300	25,036
Total Interest Income Recognized	340	222	637	514
Total Cash Basis Income Recognized	338	219	568	437
Commercial Loans [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	6,252	5,120	6,252	5,120	4,758
With no specific allowance recorded, Recorded Investment	2,801	1,044	2,801	1,044	300
With no specific allowance recorded, Average Recorded Investment	1,464	988	1,076	1,007
With no specific allowance recorded, Interest Income Recognized	16	1	18	4
With no specific allowance recorded, Cash Basis Income Recognized	16	1	18	4
With a specific allowance recorded, Unpaid Principal Balance	5,654	2,476	5,654	2,476	2,175
With a specific allowance recorded, Recorded Investment	4,879	2,075	4,879	2,075	1,717
With a specific allowance recorded, Allowance for Loan Losses Allocated	857	514	857	514	103
With a specific allowance recorded, Average Recorded Investment	4,015	2,161	3,248	2,210
With a specific allowance recorded, Interest Income Recognized	134	22	182	52
With a specific allowance recorded, Cash Basis Income Recognized	134	22	174	44
Commercial Loans [Member] | Multifamily [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	155	28	155	28	443
With no specific allowance recorded, Recorded Investment					170
With no specific allowance recorded, Average Recorded Investment			57
With no specific allowance recorded, Interest Income Recognized			1
With no specific allowance recorded, Cash Basis Income Recognized			1
With a specific allowance recorded, Unpaid Principal Balance		422		422
With a specific allowance recorded, Recorded Investment		275		275
With a specific allowance recorded, Allowance for Loan Losses Allocated		28		28
With a specific allowance recorded, Average Recorded Investment		275		275
Commercial Loans [Member] | Nonresidential [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	2,942	630	2,942	630	588
With no specific allowance recorded, Recorded Investment	2,801	137	2,801	137	130
With no specific allowance recorded, Average Recorded Investment	1,464	78	1,019	100
With no specific allowance recorded, Interest Income Recognized	16	1	17	4
With no specific allowance recorded, Cash Basis Income Recognized	16	1	17	4
With a specific allowance recorded, Unpaid Principal Balance		1,235		1,235	1,186
With a specific allowance recorded, Recorded Investment		1,232		1,232	1,186
With a specific allowance recorded, Allowance for Loan Losses Allocated		13		13	12
With a specific allowance recorded, Average Recorded Investment	1,359	1,323	1,301	1,356
With a specific allowance recorded, Interest Income Recognized		22	45	52
With a specific allowance recorded, Cash Basis Income Recognized		22	37	44
Commercial Loans [Member] | Land [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance		706		706
With no specific allowance recorded, Average Recorded Investment		5		6
Commercial Loans [Member] | Construction [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	2,446	2,457	2,446	2,457	2,447
Commercial Loans [Member] | Secured [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	235	1,115	235	1,115	806
With no specific allowance recorded, Recorded Investment		907		907
With no specific allowance recorded, Average Recorded Investment		905		901
With a specific allowance recorded, Unpaid Principal Balance	5,654	819	5,654	819	989
With a specific allowance recorded, Recorded Investment	4,879	568	4,879	568	531
With a specific allowance recorded, Allowance for Loan Losses Allocated	857	473	857	473	91
With a specific allowance recorded, Average Recorded Investment	2,656	563	1,947	579
With a specific allowance recorded, Interest Income Recognized	134		137
With a specific allowance recorded, Cash Basis Income Recognized	134		137
Commercial Loans [Member] | Unsecured [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	474	184	474	184	474
Residential Mortgage Loans [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	5,579	6,918	5,579	6,918	5,840
With no specific allowance recorded, Recorded Investment	4,792	5,994	4,792	5,994	4,908
With no specific allowance recorded, Average Recorded Investment	4,554	5,683	4,672	5,602
With no specific allowance recorded, Interest Income Recognized	35	30	64	74
With no specific allowance recorded, Cash Basis Income Recognized	35	30	55	58
With a specific allowance recorded, Unpaid Principal Balance	7,741	8,574	7,741	8,574	8,298
With a specific allowance recorded, Recorded Investment	7,610	8,461	7,610	8,461	8,178
With a specific allowance recorded, Allowance for Loan Losses Allocated	669	834	669	834	798
With a specific allowance recorded, Average Recorded Investment	8,027	9,340	8,077	9,793
With a specific allowance recorded, Interest Income Recognized	92	98	239	233
With a specific allowance recorded, Cash Basis Income Recognized	91	96	202	195
Residential Mortgage Loans [Member] | One-to Four-Family [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	5,579	6,918	5,579	6,918	5,840
With no specific allowance recorded, Recorded Investment	4,792	5,994	4,792	5,994	4,908
With no specific allowance recorded, Average Recorded Investment	4,554	5,683	4,672	5,602
With no specific allowance recorded, Interest Income Recognized	35	30	64	74
With no specific allowance recorded, Cash Basis Income Recognized	35	30	55	58
With a specific allowance recorded, Unpaid Principal Balance	7,741	8,574	7,741	8,574	8,298
With a specific allowance recorded, Recorded Investment	7,610	8,461	7,610	8,461	8,178
With a specific allowance recorded, Allowance for Loan Losses Allocated	669	834	669	834	798
With a specific allowance recorded, Average Recorded Investment	8,027	9,340	8,077	9,793
With a specific allowance recorded, Interest Income Recognized	92	98	239	233
With a specific allowance recorded, Cash Basis Income Recognized	91	96	202	195
Consumer Loans [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	1,814	2,599	1,814	2,599	2,203
With no specific allowance recorded, Recorded Investment	1,105	1,527	1,105	1,527	1,291
With no specific allowance recorded, Average Recorded Investment	1,070	1,440	1,144	1,429
With no specific allowance recorded, Interest Income Recognized	8	8	11	15
With no specific allowance recorded, Cash Basis Income Recognized	8	8	10	14
With a specific allowance recorded, Unpaid Principal Balance	4,049	4,770	4,049	4,770	4,295
With a specific allowance recorded, Recorded Investment	3,952	4,677	3,952	4,677	4,200
With a specific allowance recorded, Allowance for Loan Losses Allocated	290	313	290	313	300
With a specific allowance recorded, Average Recorded Investment	4,026	4,821	4,083	4,995
With a specific allowance recorded, Interest Income Recognized	55	63	123	136
With a specific allowance recorded, Cash Basis Income Recognized	54	62	109	122
Consumer Loans [Member] | Home Equity [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	1,041	1,496	1,041	1,496	1,084
With no specific allowance recorded, Recorded Investment	926	1,224	926	1,224	957
With no specific allowance recorded, Average Recorded Investment	889	1,101	912	1,087
With no specific allowance recorded, Interest Income Recognized	6	6	7	11
With no specific allowance recorded, Cash Basis Income Recognized	6	6	6	10
With a specific allowance recorded, Unpaid Principal Balance	3,620	4,282	3,620	4,282	3,925
With a specific allowance recorded, Recorded Investment	3,535	4,201	3,535	4,201	3,842
With a specific allowance recorded, Allowance for Loan Losses Allocated	274	295	274	295	283
With a specific allowance recorded, Average Recorded Investment	3,600	4,338	3,680	4,505
With a specific allowance recorded, Interest Income Recognized	49	57	110	123
With a specific allowance recorded, Cash Basis Income Recognized	48	56	97	110
Consumer Loans [Member] | Auto [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	33	29	33	29	25
With no specific allowance recorded, Recorded Investment	25	22	25	22	17
With no specific allowance recorded, Average Recorded Investment	20	42	19	33
Consumer Loans [Member] | Marine [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	354	553	354	553	502
With no specific allowance recorded, Recorded Investment	105	181	105	181	145
With no specific allowance recorded, Average Recorded Investment	105	181	118	181
With a specific allowance recorded, Unpaid Principal Balance	86	95	86	95	91
With a specific allowance recorded, Recorded Investment	86	95	86	95	91
With a specific allowance recorded, Allowance for Loan Losses Allocated	1	1	1	1	1
With a specific allowance recorded, Average Recorded Investment	88	96	89	97
With a specific allowance recorded, Interest Income Recognized	1	1	2	2
With a specific allowance recorded, Cash Basis Income Recognized	1	1	2	2
Consumer Loans [Member] | Recreational Vehicle [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance	386	520	386	520	592
With no specific allowance recorded, Recorded Investment	49	100	49	100	172
With no specific allowance recorded, Average Recorded Investment	56	108	95	122
With no specific allowance recorded, Interest Income Recognized	2	2	4	4
With no specific allowance recorded, Cash Basis Income Recognized	2	2	4	4
With a specific allowance recorded, Unpaid Principal Balance	343	393	343	393	279
With a specific allowance recorded, Recorded Investment	331	381	331	381	267
With a specific allowance recorded, Allowance for Loan Losses Allocated	15	17	15	17	$ 16
With a specific allowance recorded, Average Recorded Investment	338	387	314	393
With a specific allowance recorded, Interest Income Recognized	5	5	11	11
With a specific allowance recorded, Cash Basis Income Recognized	$ 5	5	$ 10	10
Consumer Loans [Member] | Other [Member]
Financing Receivable Impaired [Line Items]
With no specific allowance recorded, Unpaid Principal Balance		1		1
With no specific allowance recorded, Average Recorded Investment		$ 8		$ 6